The invention relates generally to welding techniques, and more particularly to improved automated welding processes. The present disclosure is related to previously filed U.S. patent application Ser. No. 13/767,392, entitled “Adaptable Rotating Arc Welding Method and System,” filed on Feb. 14, 2013, which is hereby incorporated into the present disclosure by reference. The present disclosure also incorporates U.S. patent application Ser. No. 13/526,278, entitled “Metal Cored Welding Method and System,” filed on Jun. 18, 2012, and U.S. patent application Ser. No. 13/681,687, entitled “DC Electrode Negative Rotating Arc Welding Method and System,” filed on Nov. 20, 2012.
A range of techniques have been developed for joining workpieces by welding operations. These include diverse processes and materials, with most modern processes involving arcs developed between a consumable or non-consumable electrode and the workpieces. Welding processes with non-consumable electrodes may include tungsten inert gas (TIG) welding processes, which employ a non-consumable tungsten electrode that is independent from the filler material. The processes are often grouped in such categories as constant current processes, constant voltage processes, pulsed processes, and so forth. However, further divisions between these are common, particularly in processes that consume an electrode to add filler metal to the weld. In virtually all such cases, the process selected is highly linked to the filler material and its form, with certain processes exclusively utilizing a particular type of electrode. Exemplary processes include, but are not limited to, metal inert gas (MIG) welding and pulsed gas metal arc welding (GMAW-P), both of which form part of a larger group sometimes referred to as gas metal arc welding (GMAW). In addition, in certain embodiments, other types of welding processes, such as metal active gas (MAG) processes, flux-cored arc welding (FCAW) processes, metal-cored arc welding (MCAW) processes, and so forth, may be implemented.
In GMAW welding, an electrode in the form of a wire is consumed by the progressing weld pool, melted by the heat of an arc between the electrode wire and the workpiece. The wire is continuously fed from a spool through welding torch where a charge is imparted to the wire to create the arc. The electrode types used in these processes are often referred to as either solid wire, flux cored or metal cored. Each type is considered to have distinct advantages and disadvantages over the others, and careful adjustments to the welding process and weld settings may be required to optimize their performance. For example, solid wire, while less expensive than the other types, is typically used with inert shielding gases, which can be relatively expensive. Flux cored wires may not require separate shielding gas feeds, but are more expensive than solid wires. Metal cored wires do require shielding gas, but these may be adjusted to mixes that are sometimes less expensive than those required for solid wires.
All three of these electrode types may be used with different transfer modes, referring to the mechanical and electromechanical phenomena of moving metal from the electrode tip to the progressing weld bead. A number of such transfer modes exist, such as short circuit transfer, globular transfer, spray transfer, and pulsed spray (e.g., droplet) transfer. In practice, transfer physics may appear as a hybrid of these, and the actual material transfer may transition between them during welding, although the process and electrode are often selected to maintain a certain transfer mode. In general, the material transfer may be assisted by the centrifugal force of the radial movement of the electrode 44 and, in certain embodiments, in combination with mechanical inertia of liquid metal at an end of the electrode 44 when axial movement of the electrode 44 slows in forward movement (i.e., toward the workpiece 14) or reverses direction from forward movement (i.e., toward the workpiece 14) to reverse movement (i.e., away from the workpiece 14), as described in greater detail below.
As the torch progresses and consumes the wire it leaves behind a deposit of filler material between the two workpieces known as a weld bead. In general the width of the weld bead created during the transfer mode is seen as a function of several operative parameters. Depending on the fit-up between the workpieces, the weld bead width may or may not be adequate to ensure the integrity of the finished welded product. To avoid this, a welding operator must visually detect the fit-up for any workpiece gaps prior to welding and compensate manually to ensure the integrity of the welded piece. However, automated welding systems lack this intelligent consideration and may not be tolerant of fit-up gaps beyond a narrow tolerance range. Moreover, excess heat applied to relatively thin portions of the workpieces and/or to the weld bead may form holes in the weld bead. This may result in weld defects, manual reworking, and ultimate rejection of finished welded parts.
Manufacturers are constantly looking for new ways to improve automated welding methods, increase the success rate of the welded pieces, and speed up the manufacturing process overall. However, current automated welding techniques coupled with the increased speed of the processes that manufacturers have come to rely on can result in many finished workpieces with poor fit-up.